As a carburizing device that heats a metal material, which is a treatment object, to perform carburization treatment on the treatment object, a vacuum carburizing furnace is known (for example, refer to Patent Documents 1 and 2).
A vacuum carburizing furnace is an apparatus that performs vacuum carburization treatment using hydrocarbon-based gas (carburizing gas) at high temperature and reduced pressure, and the vacuum carburization treatment is treatment in which carburization is caused by decomposing hydrocarbon-based gas into carbon and hydrogen and making a carbon component react on the surface of steel.
In such vacuum carburization treatment, hydrocarbon-based gas is decomposed into carbon and hydrogen at high temperature and reduced pressure, and also a polymerization reaction that forms polymeric substances may be caused. Additionally, the decomposed carbon may cause sooting. If products such as polymeric substances or soot adheres to and is deposited on the inside of the furnace, particularly on the surface of a heater as a heating source, the heating function of the heater degrades, and excellent carburization treatment cannot be performed. As a result, excessive energy, time, and the like are required for the carburization treatment.
In the related art, Patent Document 1 discloses that, in order to prevent such degradation of adiabatic performance, an operation termed burnout of introducing air into the furnace to burn products such as soot is performed.
Additionally, Patent Document 2 discloses that products such as polymeric substances or soot are prevented from adhering to the surface of an electric heater as a heat source by covering the electric heater with a radiant tube made of a ceramic.
Additionally, Patent Documents 3 to 5 disclose a heat-treating furnace and a heating type furnace that have a heater installed in a protective tube.